High resolution spatial light modulation

ABSTRACT

Methods and apparatus for providing a high-resolution spatial light modulator. A spatial light modulator includes a cell that includes: a substrate portion; a first support post and a second support post, each having a top surface; and a micro mirror. The micro mirror includes a bottom layer that includes a hinge member having a longitudinal axis, a width across the longitudinal axis, a first end on the longitudinal axis, and a second end on the longitudinal axis. The first end and second end is secured to the first support post and the second support post, respectively. The hinge member has a same thickness of the bottom layer, wherein the width of the hinge member is greater than a thickness of the bottom layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. Section 120 of U.S. application Ser. No. 11/346,661,(“the '661 application”) which was filed on Feb. 3, 2006, which is acontinuation-in-part application of U.S. patent application Ser. No.10/974,468, entitled “High Contrast Spatial Light Modulator And Method”,which was filed on Oct. 26, 2004, now U.S. Pat. No. 7,167,298, whichclaims the benefit of priority of U.S. Provisional Application No.60/514,589, filed Oct. 27, 2003. The '661 application is also acontinuation-in-part application of U.S. patent application Ser. No.10/974,461, entitled “High Contrast Spatial Light Modulator”, which wasfiled on Oct. 25, 2004, now U.S. Pat. No. 7,245,415, which claims thebenefit of priority of U.S. Provisional Application No. 60/513,327 filedOct. 23, 2003. The disclosure of each prior application is consideredpart of and is incorporated by reference in the disclosure of thisapplication.

BACKGROUND

The present disclosure relates to spatial light modulators.

In general, a spatial light modulator (SLM) includes an array of cells,each of which includes a micro mirror that can be tilted about an axisand, furthermore, circuitry for generating electrostatic forces thatoperate to tilt the micro mirror. In addition, a cell typically includesstructures that hold and allow the tilting of the micro mirror. Inconventional SLMs, there are gaps between cells for accommodating suchstructures. The cell usually further includes a first structure and asecond structure configured to mechanically stop the cell's micro mirrorat the “on” position and the “off” position, respectively. Thesestructures are referred to as mechanical stops.

In one implementation, for example, a digital mode of operation fordisplaying video images, there are two positions at which the micromirror can be tilted. In an “on” position or state, the micro mirrordirects incident light to an assigned pixel of a display. In an “off”position or state, the micro mirror directs incident light away from theassigned pixel. The “on” position can be, for example, 20 degrees fromthe horizontal in a first direction of rotation about the axis, and the“off” position can be, for example, 15 degrees from the horizontal inthe opposite direction.

An SLM implemented as described above generally operates by tilting aselected combination of micro mirrors to selectively project light todisplay an image on the display. A display that implements SLMtechnology is typically required to refresh images at high frequenciestypical of video applications. Each instant of refreshing can includechanging the state of all or some of the micro mirrors. Providing a fastresponse by the micro mirrors therefore can be crucial to the properoperation of an SLM-based display device. One issue with response timeis related to the stiction, i.e., surface contact adhesion, between thelower surface of the mirror and the mechanical stop in contact with thesurface. Stiction can cause a delay in the mirror's response or may evenprevent the mirror from changing state.

SUMMARY

In one general aspect, the invention features a spatial light modulator,a cell of which includes: a substrate portion; a first support post anda second support post, each having a top surface; and a micro mirror.The micro mirror includes a bottom layer that includes a hinge memberhaving a longitudinal axis, a width across the longitudinal axis, afirst end on the longitudinal axis, and a second end on the longitudinalaxis. The first end and second end is secured to the first support postand the second support post, respectively. The hinge member has a samethickness of the bottom layer, wherein the width of the hinge member isgreater than a thickness of the bottom layer.

In another general aspect, the invention features a method for making aspatial light modulator. The method includes: forming a controlsubstrate; forming a first and a second support posts situated on top ofthe substrate; forming a layer of amorphous silicon a bottom layer byvapor deposition of amorphous silicon, wherein a thickness of the layeris controlled by controlling the vapor deposition; and patterning thelayer to form a bottom layer of a micro mirror. The bottom layerincludes a hinge member about which the micro mirror is configured totilt. The hinge member includes a first end secured to the first supportpost. The hinge member includes a second end secured to the secondsupport post.

Particular embodiments of the invention can be implemented to realizeone or more of the following advantages. Methods and apparatus describedin the present specification provide an SLM in which gaps between cellsare reduced or minimized. For each cell, structures for holding a micromirror and for allowing its tilting are completely hidden underneath themicro mirror. There are no structures, for example, conventional walls,used for supporting the micro mirror, that protrude beyond the perimeterof the micro mirror. Gaps between cells of the described SLM, unlike inconventional SLMs, need not accommodate these protruding structures and,hence, can be reduced or minimized. The described SLM can include morecells per unit area and, consequently, generate images havingresolutions superior to conventional SLMs.

Methods and apparatus described provide an SLM in which a mechanicalfeature by which a micro mirror of a cell is tilted can act as atorsional spring that positions the micro mirror in a neutral or flatposition in the absence of external forces and, furthermore, thatprovides torsional forces that aid in overcoming stiction between themicro mirror and a landing tip with which the micro is in contact whenthe micro mirror is being repositioned from one state to another.Moreover, the mechanical feature can be manufactured to precisedimensions and, hence, can have an exact spring constant. The springconstants of the cells of the described SLM consequently do not varygreatly, which great variance can cause unreliable operation. Amechanical feature that is too thick and have a spring constant that istoo high, for example, would not allow its micro mirror to be moved fromthe neutral position to either the on or off state. A mechanical featurethat is too thin and have a spring constant that is too low, on theother hand, may not provide sufficient aid to overcome stiction when themicro mirror is being repositioned from one state to another. Thedescribed SLM thus improves reliability of operation.

Furthermore, methods and apparatus described provide an SLM in whichgaps between a reflective surface of a micro mirror and an axis aboutwhich the micro mirror is tilted is reduced or minimized. For each cell,the mechanical feature by which the mirror is tilted, and whichconstitutes the axis about which the micro is tilted, is implemented ina bottom layer of the micro mirror. The mechanical feature and thebottom layer can be of a same thickness, which, for reasons describedbelow, can be significantly less than thicknesses typically implementedin conventional SLMs. Having a reduced or minimized gap between thereflective surface and the axis allows the micro mirror to rotatevirtually without translation, which is significant because having lesstranslation generally allows greater resolution, as described below. Thedescribed SLM can consequently generate images having resolutionssuperior to conventional SLMs.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,aspects, and advantages of the invention will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of an SLM cell.

FIG. 2 shows another perspective view of the SLM cell.

FIG. 3 shows a cross section of the SLM cell.

FIG. 4 shows another cross section of the SLM cell.

FIG. 5 shows another cross section of the SLM cell.

FIG. 6 shows an alternative implementation of the SLM cell.

FIGS. 7A and 7B show a method for making an SLM.

FIGS. 8-24 show effects of steps of the method for making the SLM.

FIGS. 25-27 show cross sections of alternative SLM implementations

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

A high contrast SLM in accordance with the invention includes threemajor portions: a bottom portion, a middle portion, and a top portion.The bottom portion of the SLM includes a substrate, which includeselectronic circuitry to control the operation of cells of the SLM. Themiddle portion of the SLM includes electrodes, vertical landing tips,and support posts for the micro mirror. The upper portion of the SLMincludes an array of micro mirrors, in each of which is implemented atorsion hinge about which the micro mirror can be titled. Thesecomponents of the SLM are further described in the following paragraphs.For ease of exhibition, only one cell of the SLM is depicted.

FIG. 1 shows a perspective view of an SLM cell 100, which includes onemicro mirror (shown as three layers 102, 104, and 106) and a portion ofthe substrate 108, on which the micro mirror, support posts 110 and 112,electrodes 114 and 116, and vertical landing tips 118 and 120 aresituated.

As depicted, the micro mirror has a sandwich structure made of threelayers 102 m 104, and 106. The micro mirror includes a middle layer 104made of amorphous silicon, which is sandwiched between an upperreflective layer 102 made of aluminum and a supportive bottom layer 106made of titanium. Alternatively, each layer can be made of a materialthat is different than that indicated. The top, middle, and bottomlayers 102, 104, and 106 are approximately 600 angstrom, 2000 to 5000angstrom, and 600 angstrom thick, respectively. Alternatively, eachlayer can have a thickness different than that indicated. The sandwichstructure improves the structural strength of the micro mirror andreduces its deformation due to, for example, temperature gradients.

The top layer 102 of the micro mirror has a top surface that isreflective. This reflective surface acts as one of many mirrors of theSLM. The bottom layer includes a hinge member 122, which includes alongitudinal axis 124, ends 126 and 128 on the longitudinal axis 124,and a width 130 across the longitudinal axis 124. The ends 26 and 128are secured to support posts 110 and 112, respectively. The middle layer104 includes a recess 132 (depicted by the phantom lines) that isconfigured to accommodate the hinge member 122. In general, the recess124 provides a gap between a top surface of the hinge member 122 and abottom surface of the middle layer 104 so that the hinge member 122 doesnot touch the middle layer 104 even when the micro mirror is tilted (andthe hinge member 122 is consequently twisted along its longitudinal axis124). The extent of the gap depends on the maximum angle at which themicro mirror is operable to tilt and, as described in the commonly ownedU.S. patent application Ser. No. 10/974,461, should be no less thanG=0.5×W×SIN(θ), where W is the cross section width of the support postand θ is the absolute value of the maximum tilt angle of the micromirror.

With the implementation described above, the natural position of themicro mirror is the position in which the micro mirror is horizontal,i.e. the quiescent state. In this position, the hinge member is nottwisted. In a sense, the spring of the hinge member is not loaded.

Also situated on the substrate portion 108 are the electrodes 114 and116 and vertical landing tips 118 and 120. To tilt the micro mirror sothat it rests on one of the vertical landing tips 118 and 120 (which iseither the “on” or the “off” state), voltage is usually supplied to andmaintained for the appropriate one of the electrodes 114 and 116 so thatan electrostatic force that is greater than the spring constant of thehinge member is generated. In such a tilted position, the hinge member122 is twisted with its center portion being tilted to the angle atwhich the micro mirror is tilted and its ends 126 and 128 (which aresecured to the support posts) remaining horizontal. The spring of thehinge member is thus loaded and there is a torsional spring effect whichurges the micro mirror back to its horizontal position. Such potentialenergy can be used to overcome stiction between the vertical landing tipon which the micro mirror is resting and the bottom surface of the micromirror.

Optionally, each vertical landing tips 118 and 120 can include a tophorizontal member to improve operation. Suitable landing tips aredescribed in commonly owned U.S. Publication No. 2007-0127110, entitled“Fast-Response Spatial Light Modulator,” which was filed on Dec. 7,2005.

The electrodes depicted are stepped. That is, each of the electrodes 114and 116 includes a first level electrode and a second level electrodethat is higher than the first level electrode. Alternatively, theelectrodes are not stepped and have only one height. Suitable electrodesare described in the commonly owned U.S. patent application Ser. No.10/974,461.

As mentioned above, the substrate portion 108 includes some of theabove-mentioned electronic circuitry. In general, the circuitry providescontrol voltages to a cell to change a state of the micro mirror of thecell. Optionally, the circuitry can implement a passive addressingscheme, in which a cell of the SLM does not require the inclusion ofactive circuit components, e.g., drivers. A suitable passive addressingscheme is described in commonly owned U.S. Publication No. 2007-0132681,entitled “Passive Micro-Array Spatial Light Modulator,” which was filedon Dec. 9, 2005.

Optionally, the cell includes a hinge support frame (not shown), whichis generally a frame that has the shape of the cell and that has a sameheight as the first level electrodes. The hinge support frame isconfigured to improve the mechanical stability of the support posts and,furthermore, retain the electrostatic potentials local to the cell. Asuitable hinge support frame is described in the commonly owned U.S.patent application Ser. No. 10/974,461.

FIG. 2 shows a perspective view of the cell 100 described above with itscomponents in place. As can be seen, the axis about which the micromirror tilts, i.e., longitudinal axis 124, runs diagonal to the edges ofthe micro mirror. The micro mirror is operable to tilt in a clockwisedirection as illustrated by an arrow 202. The micro mirror is alsooperable to tilt in a counter clockwise direction as illustrated by anarrow 204.

Notably, the support posts 110 and 112 and the hinge member 122 aresituated completely underneath the reflective top layer 102 of the micromirror. That is, these components are situated within the footprint ofthe reflective top layer of the micro mirror. A gap between adjacentcells, thus, need not accommodate any of these structures.

Moreover, the hinge member 122 is implemented so that the axis 124 aboutwhich the micro mirror tilts is located a distance less than thethickness of the micro mirror away from the reflective surface of thetop layer 102. Such an arrangement reduces the amount of translation themicro mirror undergoes when tilted to either side of the axis. A gapbetween adjacent cells, thus, need not accommodate for such atranslation of the micro mirror.

FIG. 3 shows the cross section A-A. The mirror is shown in its quiescentstate. The recess 132 in the middle layer 104 of the micro mirror isdepicted, as is the cross section of the hinge member 122 and the crosssection of the step electrodes 114 and 116. The support post 110 is alsodepicted.

FIG. 4 shows the cross section B-B. In this cross section view, therecess 132 in the middle layer 104 can be seen. Also visible are thesupport post 110, the cross section of the step electrodes 114 and 116,and the cross sections of the vertical landing tips 118 and 120. Notethat because the cross section cuts across the portion of the hingemember 122 that is attached to the rest of the bottom layer 104, thereare no gaps (depicted in FIG. 4) in the cross section of the bottomlayer 104 of the micro mirror.

FIG. 5 shows the cross section C-C. In this cross section view, the stepelectrode can be seen, as can the cross sections of the support posts.Note that the recess 132 in the middle layer 104 of the micro mirror(depicted by the phantom lines) runs across from left to right in thefigure.

In the micro mirror described above, the hinge member and, hence, theaxis about which the micro mirror tilts is diagonal to edges of themicro mirror. FIG. 6 shows an alternative implementation of the SLM inwhich the hinge member is orthogonal to edges of the micro mirror. As analternative or in addition to the diagonally hinged micro mirrordescribed above, the cell depicted can be implemented in the SLM.

FIGS. 7A and 7B show a method 700 for making the above-described SLM,and FIGS. 8-24 show effects of steps of the method depicted in FIG. 7.For ease of exhibition, only one cell of the SLM is depicted anddescribed.

A control silicon substrate 600 is formed using standard CMOSfabrication technology (step 702). In one embodiment, the controlcircuitry in the substrate includes an array of memory cells, andword-line/bit-line interconnects for communication signals. There aremany different methods to make electrical circuitry that performs theaddressing function. DRAM, SRAM, and latch devices commonly known allperform an addressing function. Because the area of a typical micromirror can be relatively large on semiconductor scales (for example, thearea of the micro mirror can have an area larger than 100 squaremicrons), complex circuitry can be manufactured beneath micro mirror.Possible circuitry includes, but is not limited to, storage buffers tostore time sequential pixel information, and circuitry to perform pulsewidth modulation conversions. FIG. 8 shows a cross sectional view of thesubstrate 600.

Using a typical CMOS fabrication process, the substrate is covered witha passivation layer 601 such as silicon oxide or silicon nitride (step704). The passivated substrate 600 is patterned and etchedanisotropically (step 706) to form a via 621 connected to theword-line/bit-line interconnects in the addressing circuitry.Alternatively, anisotropic etching of dielectric materials, such assilicon oxides or silicon nitrides, is accomplished with C₂F₆ and CHF₃based feedstock and their mixtures with He and O₂. One high selectivitydielectric etching process flows C₂F₆, CHF₃, He, and O₂ at a ratio of10:10:5:2 mixtures at a total pressure of 100 mTorr with inductivesource power of 1200 watts and a bias power 600 watts. A typical siliconoxide etch rate can reach 8000 angstroms per minute. The substrate isthen cooled with a backside helium gas flow of 20 sccm at a pressure of2 torr (step 708). FIG. 9 shows the via 621 that is formed.

An electromechanical layer 602 is deposited by PVD or PECVD depending onthe electromechanical materials selected (step 710). FIG. 10 shows thelayer deposited. This electromechanical layer 602 is patterned to definea hinge support frame 622 and a plurality of first level electrodes 623(step 712). FIG. 11 shows the effect of step 712. The patterning of theelectromechanical layer 602 is performed by the following processes.First, a layer of photoresist is spin coated to cover the substratesurface. Then, photoresist layer is exposed to standard photolithographyand is developed to form predetermined patterns. The electromechanicallayer is etched anisotropically through to form a plurality of vias andopenings. Once vias and openings are formed, residues are removed fromthe surfaces and inside the openings to clean the partially fabricatedwafer. This removal is accomplished by exposing the patterned wafer to a2000 watts of RF or microwave plasma with 2 torr total pressures of amixture of O₂, CF₄, and H₂O gases at a ratio of 40:1:5 at about 250° C.for less than five minutes. Finally, the surfaces of theelectromechanical layer are passivated by exposure to 2000 watts of RFor microwave plasma with 2 torr pressures of a 3000 sccm of H₂O vapor atabout 250° C. temperatures for less than three minutes.

A plurality of second level electrodes, a plurality of vertical landingtips, and a plurality of support posts are formed by the followingsteps. A micron thick sacrificial material 604 is deposited on thesubstrate surface, which can be spin coated photoresist or PECVD oforganic polymers (step 714). FIG. 12 shows the effect of step 714. Thesacrificial layer 604 is hardened by a series of thermal and plasmatreatments to transform the structure of the polymer materials from ahydrophobic state to hydrophilic state (step 716). First, thesacrificial layer 604 is exposed to ultraviolet light, then to a CF₄plasma for about three minutes, followed by baking sacrificial layer atabout 150° C. for about two hours before exposing the sacrificial layerto oxygen plasma for about one minute. In some cases, implanting thesacrificial layer with KeV energy of silicon, boron, or phosphors ionsfurther hardens the sacrificial layers 604.

Sacrificial layer 604 is patterned to form a plurality of via andcontact openings 632, 633, and 631 for second level electrodes, verticallanding tips, and lower portions of the support posts, respectively(step 718). FIG. 13 shows the effect of step 718. To enhance theadhesion of a subsequent electromechanical layer, the via and contactopenings are exposed to a 2000 watts of RF or microwave plasma with 2torr total pressures of a mixture of O₂, CF₄, and H₂O gases at a ratioof 40:1:5 at about 250° C. temperatures for less than five minutes.Electromechanical material 603 is then deposited to fill via and contactopenings (step 719). The filling is done by either PECVD or PVDdepending on the materials selected. For the materials selected from thegroup consisting of aluminum, titanium, tungsten, molybdenum, theiralloys, PVD is a common deposition method in the semiconductor industry.For the materials selected from the group consisting of silicon,polysilicon, silicide, polycide, tungsten, their combinations, PECVD ischosen as a method of deposition. The partially fabricated wafer isfurther planarized by CMP to a predetermined thickness slightly lessthan one micron (step 720). FIG. 14 shows the effect of steps 719 and720. The second level electrodes 635, vertical landing tips 636, andlower portions of the support posts 634 are thus formed.

After the CMP planarization, another layer of sacrificial materials 604is spin coated on the blanket surface to a predetermined thickness andhardened (step 722). FIG. 15 shows the effect of step 722. Thesacrificial layer 604 is patterned to form a plurality of contactopenings 641 for the upper portion of the support posts (step 724). FIG.16 shows the effect of step 724. Electromechanical materials aredeposited to fill vias to form the upper portions 642 of the supportposts and, furthermore, to form a bottom layer 605 of the micro mirror,i.e., the layer that includes the hinge members (step 726). The bottomlayer 605 is then planarized by CMP to a predetermined thickness (step727). The thickness of electromechanical layer 605 formed here definesthe thickness of hinge member and the mechanical performance of themirror. FIG. 17 shows the effect of steps 726 and 727.

The electromechanical layer deposited can be amorphous silicon, whichdeposition and subsequent CMP can be more precisely controlled than canetching to achieve more exactly a target thickness. (With conventionalSLMs, in which the layer at issue is typically made from single crystalsilicon, one cannot deposit and polished. Rather, because of temperatureconstraints, one must etch the layer to achieve a target thickness.)

The bottom layer is patterned and etched anisotropically to form a hingemember 644 in the bottom layer of the micro mirror (step 728). FIG. 18shows the effect of step 728. More sacrificial materials 604 aredeposited to fill the openings 643 surrounding each hinge member and toform a thin layer 604 with predetermined thickness on the surface (step730). FIG. 19 shows the effect of step 730. The thickness of the layer604 defines the depth of the recess in the middle layer of the micromirror, i.e., the extent of the spacing above each hinge member 106. Thesacrificial layer 604 is then patterned to form a sacrificial spacerabove the hinge member 644 (step 732). FIG. 20 shows the effect of step732. As discussed above, the air gap G in the recess needs to be highenough to accommodate the tilting of mirror plate 103 without touchingthe support posts 105. With an implementation in which each mirror inthe array can rotate at the maximum 15° in each direction, and in whichthe width of the support post 105 is 1.0 micron, the air gap spacing Gin the recess should be larger than 0.13 microns.

More electromechanical materials, for example, amorphous silicon, aredeposited to cover the sacrificial spacer (step 734). The newlydeposited layer is optionally planarized by CMP to a predeterminedthickness (step 736). FIG. 21 shows the effect of steps 734 and 736. Inone implementation, the thickness of the micro mirror form thus far isbetween 0.3 microns to 0.5 microns.

If the electromechanical material is aluminum or its metallic alloy, thereflectivity of mirror is high enough for most display applications. Forsome other electromechanical materials or for other applications, thereflectivity of the mirror surface may be enhanced by deposition of areflective layer 606 having a thickness of approximately 600-400angstroms or less (step 738). The electromechanical material can beselected from the group consisting of aluminum, gold, their alloys, andcombinations. FIG. 22 shows the effect of step 738. The reflectivesurface 606 of electromechanical layer is then patterned and etchedanisotropically through to form a plurality of individual mirrors (step740). FIG. 23 shows the effect of step 740.

The remaining sacrificial materials 604 are removed and residues arecleaned through a plurality of air gaps between each individual mirrorsin the array to form a functional micro-mirror array based spatial lightmodulation (step 742). FIG. 24 shows the effect of step 742.

Optionally, additional steps can be performed before delivering afunctional spatial light modulator for a video display application. Forexample, after reflective surface 606 of electromechanical layer 605 ispatterned and etched anisotropically through to form a plurality ofindividual mirrors, more sacrificial materials 604 can be deposited tocover the surface of the fabricated wafer. With its surface protected bya layer of sacrificial layer 604, the fabricated wafer goes throughcommon semiconductor packaging processes to form individual device dies.In a packaging process, the fabricated wafer is partially sawed beforeseparated into individual dies by scribing and breaking. The spatiallight modulator device die is attached to the chip base with wire bondsand interconnects before striping the remaining sacrificial materials604 and its residues in the structures. In one embodiment, the cleaningis accomplished by exposing the patterned wafer to a 2000 watts of RF ormicrowave plasma with 2 torr total pressures of a mixture of O₂, CF₄,and H₂O gases at a ratio of 40:1:5 at about 250° C. for less than fiveminutes. Finally, the surfaces of electromechanical and metallizationstructures are passivated by exposing to a 2000 watts of RF or microwaveplasma with 2 torr pressures of a 3000 sccm of H₂O vapor at about 250°C. temperatures for less than three minutes.

The SLM device die can be further coated with an anti-stiction layerinside the opening structures by exposure to a PECVD of fluorocarbon atabout 200° C. for less than five minutes before plasma cleaning andelectro-optical functional testing. Finally, the SLM device can behermetically sealed with a glass window lip and sent to burn-in processfor reliability and robust quality control.

FIGS. 25-27 each show a partial cross section of an alternativeimplementation of the SLM cell depicted in FIGS. 1-3. The cross sectionsare taken along the same lines as those of cross section A-A (FIG. 1).The alternative implementation depicted in FIG. 25 includes componentssimilar to those depicted inn FIG. 1, except for the middle layer. Inparticular, the middle layer 902 of the alternative implementation,unlike the middle layer 104, consists of two separate pieces 904 and 906so that the recess 908, unlike recess 132, extends completely from thetop surface of the bottom layer 106 to the bottom surface of the toplayer 102. That is, the recess 908 is a channel that is as deep as thethickness of the middle layer 902 such that a portion of the bottomsurface of the top layer 102 is exposed. With the implementation of FIG.25, the top layer 102 can be made of a reflective metal such asAluminum, the middle layer can be made of amorphous silicon or TiN_(x),and the bottom layer can be made of a conductive material such asTiN_(x).

With the implementation depicted in FIG. 26, the SLM cell includes atwo-layer rather than a three-layer micro mirror. The hinge member isimplemented in and is made of the same material as the bottom layer1002. In this implementation, the top layer 102 can be made of areflective material such as Aluminum, and the bottom layer 1002 can bemade of amorphous silicon or TiN_(x).

Like the implementation depicted in FIG. 26, the implementation depictedin FIG. 27 includes a two-layer rather than a three-layer micro mirror.However, unlike the bottom layer 1002, the bottom layer 1102 includes arecess that has a same depth as the thickness of the bottom layer sothat a portion of the bottom surface of the top layer 102 is exposed. Inthis implementation, the top layer 102 can be made of a reflectivematerial such as Aluminum, and the bottom layer 1102 can be made ofamorphous silicon, TiN_(x), or Ti.

Embodiments of the invention and all of the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of them. Embodiments of the inventioncan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on acomputer-readable medium, e.g., a machine-readable storage device, amachine-readable storage medium, a memory device, or a machine-readablepropagated signal, for execution by, or to control the operation of, adata processing apparatus. The term “data processing apparatus”encompasses all apparatus, devices, and machines for processing data,including by way of example a programmable processor, a computer, ormultiple processors or computers. The apparatus can include, in additionto hardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of them. A propagated signal is an artificially generatedsignal, e.g., a machine-generated electrical, optical, orelectromagnetic signal, that is generated to encode information fortransmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub-programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Particular embodiments of the invention have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. A same 3-dimensional multi-layerstructures may be constructed by patterning and etching theelectromechanical layers, rather than patterning the sacrificial layersand etching via. Besides video displays and printing applications, thespatial light modulator described above is also useful in otherapplications, for example, in maskless photolithography, where thespatial light modulator directs light to develop deposited photoresist,and in photonic switches, where the optical signals are directed anddistributed among fiber optical networks.

1. A method for making a spatial light modulator, the method comprising:forming a control substrate; forming a first support post and a secondsupport post on the substrate; forming a layer of amorphous silicon byvapor deposition of amorphous silicon on the substrate, wherein athickness of the layer is controlled by controlling the vapordeposition; and patterning the layer to form a bottom layer of a micromirror, the bottom layer including a hinge member about which the micromirror is configured to tilt, the hinge member having a first endsecured to the first support post and a second end secured to the secondsupport post.
 2. The method of claim 1, further comprising planarizingthe layer of amorphous silicon.
 3. The method of claim 1, furthercomprising: forming a middle layer of the micro mirror on the bottomlayer, the middle layer including a recess configured to accommodate thehinge member; and forming a reflective top layer of the micro mirror onthe middle layer.
 4. The method of claim 1, further comprising: forminga plurality of electrodes on the control substrate; and forming aplurality of vertical landing tips on the control substrate.
 5. Themethod of claim 4, wherein forming a plurality of electrodes includesforming step electrodes.
 6. The method of claim 4, wherein forming aplurality of vertical landing tips includes forming vertical landingtips having a top horizontal portion that is configured to contact thebottom layer when the micro mirror is tilted.
 7. The method of claim 1,further comprising forming a hinge support frame to buttress the supportposts, the hinge support frame being completely hidden underneath themicro mirror.